A typical hub transmission is a differential transmission with an input shaft and two output shafts. All of the hub transmission elements are rotatable, driven and carried by the motor drive shaft. The differential planetary gear transmission is considered as one of the common hub transmissions; however, it relatively expensive, heavy, and it has a significant loss of efficiency (about 3% per stage). On the contrary, hub planetary belt transmission is relatively inexpensive, light, and may have significantly higher efficiency (e.g. higher than 98% efficiency for the flat belts), per reduction stage.
U.S. Pat. No. 8,876,648 in the name of the present Applicant discloses a planetary belt transmission with a motor drive having a motor drive shaft, a distributing pulley attached to the motor drive shaft and a collecting pulley attached to an output shaft. Two or more distributing belts are coupled to the distributing pulley and two or more collecting belts are coupled to the collecting pulley from mutually opposite radial directions. Four or more transmitting pulleys are arranged in two or more concentric pairs around the distributing pulley and the collecting pulley and are coupled to the distributing pulley and the collecting pulley via the distributing belts and the collecting belts, respectively. Two or more peripheral shafts support the transmitting pulleys, while allowing movement in a radial direction only relative to the output shaft and being preloaded so as to apply a net zero radial force on the distributing pulleys and the collecting pulleys in a plane perpendicular to respective axes thereof. In use the housing is restrained and the output shaft rotates.